The number of domestic Web sites that have been attacked by foreign hackers has been on the increase for three consecutive months, sparking concerns for the nation’s cyber security, according to the Ministry of Information and Communication on Tuesday.

The ministry reported that in August, overseas hackers attacked 287 Web sites in South Korea, up from 262 in July and 172 in June.

On Aug. 11, about 70 domestic Web sites were attacked by a group of Brazilian hackers called ``int3rc3ptOr.’’ The group also attacked 120 Web sites on Aug. 15 and 40 more on Aug. 16, the ministry said.

Moreover, an Indonesian hacker group called ``neotector’’ attacked seven computer servers. The group called ‘`Mirror’’ and the other one called ``Hack3rz’’ have been reported to have transformed 100 domestic Web sites and 10 Web sites respectively.

The ministry called for tighter cyber security by applying patch files and reinforcing passwords, in preparation for such accidents.

South Korea boasts about one of the world's highest broadband Internet penetration rates with more than 11 million people connected to the always-on, high-speed Internet.

According to experts, although South Korea has the most advanced Internet network in the world, its cyber security is weak compared to the United States and other industrial nations.